Project Summary/Abstract Tungsten is an emerging toxicant, due to increased human exposure, yet limited knowledge of the human health risks. One large research gap is our lack of knowledge of the carcinogenic/tumorigenic risks of tungsten exposure. Importantly, a few in vivo studies do suggest that tungsten can enhance tumor promotion. However, more research is needed to determine which forms and routes of exposure of tungsten can drive tumorigenesis and the underlying cellular/molecular mechanisms of action. An accidental exposure of breast cancer patients to tungsten following experimental radiotherapy, prompted us to investigate the role of tungsten on breast cancer progression and metastasis, by conducting an animal study using an aggressive orthotopic mammary cancer mouse model. Oral tungstate exposure enhanced breast cancer metastasis to the lung and increased growth at the metastatic site. Interestingly, tungsten-enhanced metastasis was associated with enhanced stroma in the tumor microenvironment, importantly, cancer-associated fibroblasts (CAFs) that are known to drive tumor progression. Our research identified, for the first time, a potential cellular mechanism of action for tungsten-enhanced tumor promotion. However, what role the CAFs plays in this complex process remains to be elucidated. This proposal will use a novel, integrative approach to investigate when and how tungsten targets the tumor microenvironment to promote breast cancer. AIM 1 I will evaluate how different forms of tungsten (oral tungstate, inhaled tungsten carbide and implantation tungsten metal fragments) target the tumor microenvironment to affect breast cancer progression from initiation to metastasis. I will extend my initial findings to determine how different forms of tungsten alter breast cancer development, growth and metastasis to multiple sites including lung, liver, bone, and brain. AIM 2, I will measure CAF activation following tungsten exposure in vitro. I will address the following questions. Can tungsten enhance CAF activation from stromal precursors? Do tungsten-exposed CAFs enhance tumor cell invasion, growth, and immune cell recruitment? And, does tungsten alter tumor cell cues to enhance CAF activation and/or recruitment? Finally, in AIM 3 I will test the impact of tungsten-altered CAFs to enhance metastasis in an in vivo model. I will determine if tungsten-altered CAFs promote metastasis and growth in the lung niche by answering the following questions. What is the source of tungsten-enhanced CAFs in the lung niche? Do CAFs from the lung niche of tungsten- exposed tumor-bearing mice have an altered cytokine/chemokine profile? And, are CAFs critical mediators of tungsten-enhanced lung metastasis? Completion of this proposal will extend our toxicological knowledge of tungsten to determine how different forms of tungsten impact breast cancer progression and define the role of the tumor microenvironment, particularly CAFs in tungsten-enhanced breast tumorigenesis. This work will also identify a novel cellular mechanism of action that can expand our knowledge of how environmental toxicant can drive tumorigenesis and develop new therapeutic interventions.